There is a market in which a piezoelectric material composed of an ABO3 perovskite-type oxide is used as an ink jet head or an ultrasonic transducer. The piezoelectric material used in the field is mainly lead zirconate titanate (PZT).
However, PZT contains lead as an element in the A site and is thus considered problematic for its influence on the environment. Accordingly, piezoelectric materials using lead-free perovskite-type oxides have been proposed.
As piezoelectric materials consisting of lead-free perovskite-type oxides, those materials including Bi as an element in the A site have been extensively studied. For example, Bi (Zn0.5, Ti0.5) O3 is described in Matthew R. Suchomel, et al. in Chem. Mater. 2006, 18, 4987-4989. According to a theoretical calculation in simulations, Bi (Zn0.5, Ti0.5) O3 has been reported to have high piezoelectric properties or a high Curie temperature. However, the poling procedure of Bi (Zn0.5, Ti0.5) O3 has been known to be difficult, and there is no example of reports in which its poling procedure was successfully achieved and its piezoelectric characteristics and Curie temperature were actually measured. The difficulty in poling procedure of Bi (Zn0.5, Ti0.5) O3 is considered attributable to its high Curie temperature and high anisotropy (c/a=1.21), but the reason for the difficulty is not revealed.
Because of the difficulty in poling procedure of Bi (Zn0.5, Ti0.5) O3, expected high piezoelectric characteristics cannot be exhibited, thus making its applications limited.
H. Nagata, et al., Ceramic Transactions, Vol. 167, No. 2, pp. 213 to 221, 2005 have described (Bi0.5, Na0.5) TiO3, that is, a material having Bi and Na employed as a composite in the A site.
However, although (Bi0.5, Na0.5) TiO3 exhibits excellent piezoelectric characteristics at or near room temperature, there is a problem that it shows abrupt degradation in the piezoelectric characteristics at 150° C. or more and is therefore not suitable for use in devices that operate at high temperatures.
Further, when an alkali metal is contained as a component in a piezoelectric body, the piezoelectric body when used as a thin film is not suitable for silicon process because of its deliquescency or the like, thus posing the problem of durability as a bulk piezoelectric body used in devices such as piezoelectric transducers. Accordingly, the piezoelectric material is desirably free from an alkali metal.
The present invention has been accomplished in light of such background art and provides a piezoelectric material having a high Curie temperature and solving the difficulty in poling procedure, employing a Bi-based piezoelectric body which is excellent in performance as the piezoelectric body.